This project is aimed at characterizing the mechanisms regulating voltage- activated calcium channels and identifying the structures involved in the translation of membrane voltage to channel opening. A number of processes such as muscle contraction and neurotransmitter release are tightly coupled to the influx of calcium through voltage-activated calcium channels. The time course and magnitude of these responses are determined by the often complex behavior of these channels. For instance, when the cell membrane depolarizes, some channels open once or twice for a fraction of a millisecond, others open repeatedly in a burst lasting tens of milliseconds and still others never open. It is not known whether there are structural differences, transient or permanent, between channel proteins that open in different manners. We do know however, that the frequency of isolated brief events relative to burst or failure to open is regulated by neurotransmitters or hormones. Adrenergic potentiation of calcium influx for example, through phosphorylation of the channel protein, increases the frequency of openings in the burst mode and a decrease in the frequency of failures to open. This project is aimed at characterizing the molecular components associated with the different modes of channel opening and helps establish the structure or structures connecting the voltage-induced movement of charged elements to the opening of an ion selective pore. To this and I will measure ionic currents through open channels and how they relate to charge movements. These signals will be recorded in isolation by expressing calcium channel protein in Xenopus oocytes and, through mutagenesis, participating structures will be identified. Additional insights in the molecular mechanisms controlling channel opening will be gained by studying modulation by the different subunits of the ion-channel protein complex. Macroscopic calcium currents will be recorded with a novel technique that allows the recording of the charge movement with extended resolution. The energetic of the open-state and neighboring conformational state of the channel protein will be studied through single- channel recordings using standard patch clamp technique. Regulation of intracellular calcium is important to the control of the contractile machinery of cells of the cardiovascular system and skeletal muscles. They also control hormone secretion and inter neuronal communication. Gaining insight on the structural elements determining calcium channel behavior may lead to the development of new therapeutical strategy aimed at controlling calcium influx. The importance of calcium channels i health and disease can be illustrated by the wide use of calcium channel blocker in the treatment of chest pain, arrhythmia and hypertension. In some autoimmune diseases such as amyotropic lateral sclerosis r type I diabetes, targeted cells are driven to aptotosis or programmed cell death by an increase in calcium influx through voltage activated channels.